During the recess, victims of gun violence rallied outside Flake's Phoenix headquarters and begged him to come out and talk.

Caren Teves, whose son Alex died in the Aurora, Colo., movie theater shootings, said she wrote to Flake before April's gun vote. She and her husband asked Flake to visit their dining room in Phoenix to see Alex's empty chair at the table. Flake responded with a letter of his own, saying he supported stronger background checks. But then he voted against them.

"After receiving this letter, I would expect Sen. Flake to look me in the eye and explain why he ignored me, why he ignored my husband and my family," Teves said.

After speaking at the rally, Teves walked to Flake's office door with a victim of the 2011 Tucson shootings. She went inside and emerged a minute later, discouraged.

"He apparently is in the state traveling," she said. "He's not in his office today. I also requested another meeting. Again. I can't even count the number of times I've requested a meeting. No response."

Teves is not alone in her frustration.

"It's really unusual for us to see a senator become this unpopular this quickly," says Tom Jensen of Public Policy Polling, the left-leaning group that crowned Flake most unpopular.

After all, Flake was just elected in November. After the gun debate, Jensen's poll found a big drop in popularity among senators in Alaska, Ohio and Nevada. The biggest blow came in Arizona, where 70 percent of voters say they want background checks on all gun sales. More than half now say they're less likely to vote for Flake because of his vote on the measure.

"When you kind of add that all into the pot together, he's really done something to antagonize most voters across the ideological spectrum, and that's how you end up with approval numbers like this," Jensen says.

Flake says he has not ignored his constituents on the gun debate and he has explained why he voted against the measure written by his colleagues Sen. Joe Manchin, D-W.Va., and Sen. Pat Toomey, R-Pa.

"I mean it when I say I think we need to strengthen background checks. But people can't assume that the Manchin-Toomey proposal as it was structured is the only avenue to do that," Flake says.

Flake says their bill was too broad. He worried that the language would restrict private gun sales, especially in rural areas. He says he would vote for a different proposal that focuses more on keeping the mentally ill from getting guns.

"Legislation language matters," he says. "When you're in the Senate in particular, you're supposed to pay close attention to that."

Flake says navigating the demands of an entire state in the Senate has been tough — tougher than his 12-year stint in the House representing a single Republican district. But as work resumes in Congress this week, he says he hopes a new gun bill will eventually emerge.